1. Field of the Invention
The present invention relates to objects constructed of silicon carbide such as a spin-coater used in semiconductor manufacturing equipment and optical elements such as soft X-ray reflectors (reflecting mirrors).
2. Description of the Prior Art
Objects constructed of silicon carbide, which are formed of sintered silicon carbide alone or formed as composite body of sintered silicon carbide coated with silicon carbide film, are finding use widely in equipment and component parts in various industrial and technical fields because of the outstanding features of silicon carbon, including a high degree of corrosion resistance, thermal conductivity, and wear resistance. Among the fields of use are semiconductor manufacturing equipment such as spin-coater, optical elements such as soft X-ray reflectors, and equipment and component parts in many different applications.
Silicon carbide film is especially excellent in physical and optical properties. It is used as an essential component part of objects constructed of silicon carbide in areas where the sintered silicon carbide alone cannot attain performances required of the silicon carbide object. It is also used where it is desired to further improve the performances exhibited by sintered silicon carbide. Silicon carbide film is formed on, for example: the wafer supporting surface of a spin-coater to be used for spin-coating of wafers where sticking of impurities has to be prevented at any cost (where the wafer must be protected from contamination); the reflective surface of soft X-ray reflector where a high degree of smoothness is required; and the area where a required high sealing air-tightness cannot be attained by porous sintered silicon carbide material.
The form of an object of constructed of silicon carbide (referred to as "the form of the constructed object" hereinafter) is mainly determined by the form of sintered silicon carbide, not only in the case where the object constructed of silicon carbide is made up of sintered silicon carbide alone but also in the case where it is a composite body with the surface of sintered silicon carbide coated with silicon carbide film. Hence, it is necessary to shape sintered silicon carbide in accordance with the form of the constructed object (that is, in a form identical or roughly identical with the form of the constructed object).
There is, however, a certain limit to the form of sintered silicon carbide that is obtained by forming and burning silicon carbide sintering material (silicon carbide powder or silicon carbide powder with a suitable binder mixed therewith). Sintered silicon carbide beyond that limit can not be obtained by sintering, that is, forming and heating alone. Thus, while sintered silicon carbide components in simple forms such as plate, bar, and cylinder can be produced by forming and heating alone, complicated forms such as those having portions of substantially differing thicknesses cannot be formed by forming and heating alone. In sum, a complicated form of the constructed object, which is determined by the form of sintered silicon carbide, has presented the following problems with manufacturing costs and application.
In the case where the form of the constructed object has both thick and thin portions, for example, sintered silicon carbide with a form corresponding to the form of the constructed object cannot be obtained by forming and heating alone but also additionally requires cutting and grinding. Thus, silicon carbide is first sintered to meet a desired size of the thick portion. The silicon carbide thus sintered is then cut and ground to a desired shape. This method naturally, therefore, presents some problems such as low production efficiency and increased manufacturing processes. Manufacturing economies deteriorate as the size differential between the thick portion and the thin portion (thickness difference) is increased or the relative amount of the thin portion is increased.
Another problem is that portions of sintered silicon carbide with silicon carbide film coated on the surface could deform or warp when the silicon carbide film is formed on the surface of the sintered silicon carbide. This is especially the case with thin portions; thick portions generally present no such problem. Thus, there is concern that the coated thin portion will warp when subjected to a high temperatures in application, because of the difference in coefficient of thermal expansion between the coated thin portion and the silicon carbide coat.
A further problem is that an object constructed of silicon carbide cannot be employed for uses in which, although application of an object constructed of silicon carbide would be desirable, the form of the object to be constructed is one which cannot be shaped by forming and heating silicon carbide sintering material nor by cutting (for instance, a hollow box shape). That is to say, use of silicon carbide is greatly limited by the required form of the constructed object.